The great Yanshanian metallogenic event of eastern Asia: Consequences from one hundred million years of plate margin geodynamics

Abstract

Abstract Yanshanian (ca. 200–100 Ma) metallogeny of eastern Asia was dominantly controlled by oblique subduction and rollback of the Izanagi plate, and also, more locally in the north, by closure of the Mudanjiang Ocean basin and accretion of the Bureya-Jiamusi-Khanka block and the Sikhote-Alin terranes. Although exact distances are difficult to estimate due to Early Cretaceous crustal extension, ores related to Yanshanian subduction certainly developed for more than 1500 km landward from the active trench, such as exemplified by those deposits overprinting the Paleoproterozoic Trans-North China orogen. In the northern part of the Yanshanian orogen, and thus hosted within the eastern edge of the Central Asian orogenic belt, Endako-type porphyry Mo deposits related to subduction of the Mudanjiang slab formed throughout northeast China from 200 to 135 Ma. Extensional magmatism related to rollback of the slab led to widespread Au-Ag epithermal vein development and a scattering of small Cu-Au porphyry occurrences across the same area from 125 to 100 Ma. Sinistral strike-slip motion along the continental margin in adjacent Russia, caused by the NNW motion of the Izanagi plate, led to formation of 115–95 Ma post-collisional Cu-Au porphyries, Sn-W ores associated with reduced intrusions, and orogenic gold deposits in the central Sikhote-Alin region. In the North China block, whereas early Yanshanian ore formation was relatively limited, 130–120 Ma extension-related basement uplifts were associated with formation of two of China’s most important orogenic gold provinces on the Jiaodong Peninsula and in the East Qinling; in the latter, the entire period of late Yanshanian extension may be defined by widespread 148–107 Ma Mo-rich porphyry and skarn deposit formation. To the south along the Asian margin, the oblique NW-directed subduction of the Izanagi slab was responsible for the adakitic porphyry Cu deposit formation on the eastern side of the South China block at 175–155 Ma, which continued inland for as much as 500 km to the Cathaysia-Yangtze suture. The transition at 160–150 Ma to development of the Nanling W-Sn belt in the interior of Cathaysia roughly overlaps the time of tectonic switch to slab retreat, which gradually led to seaward migration of the extension-related magmatism forming the 145–133 Ma Sn ores and 110–100 Ma high to low sulfidation epithermal deposits along the Southeast Coast belt. A period of sinistral strike-slip along the southern end of the Tan-Lu fault system was possibly responsible for a tear in the Izanagi plate and consequential S-type magmatism forming W porphyry-skarn ores of the Jiangnan belt at 145–133 Ma and I-type magmatism leading to Fe-Cu-Au skarns at the northern edge of the Yangtze block. In summary, the early Yanshanian of eastern Asia was dominated by widespread subduction-related porphyry Mo formation in the north and localized porphyry Cu formation to the south, followed by late Yanshanian development of world-class Au, Mo, Sn, and W resources during subsequent slab retreat, continental-scale extension, and strike-slip events along continental margin transform faults.